Look at your fingertips. The unmatched combinations of swirls and lines can physically identify who you are. But it took years of testing to prove that fingerprints were unique.

At the beginning of the 20th century, fingerprinting gained acceptance as a means of identification. Among the first to record their prints were civil servants and soldiers. When it came to identifying criminals, however, people were hesitant to trust that fingerprints were indeed unique. Advocates convinced juries that each print was unmistakably distinct by staging demonstrations using the jurors' own fingerprints.

As identification by fingerprint gained credibility in the courtroom during the 1930s, the number of fingerprint files grew from thousands to millions. New automated technologies improved the organization and sorting of files, enabling investigators to examine prints more efficiently. A new breed of crime fighter could now be found inside a crime lab armed with a magnifying glass and a stack of 8x8 white cards. In 1937, the first case to support a conviction based solely on fingerprint evidence took place in New York. The age of "scientific crime detection" had begun.